The present invention relates to a ratio control for a continuously variable transmission.
U.S. Pat. No. 4,735,113 issued on Apr. 5, 1988 to Yamamuro et al. discloses a ratio control of a continuously variable transmission which maintains the maximum reduction ratio in response to a shift actuator held at the corresponding maximum reduction ratio position, but effects an upshift from the maximum reduction ratio in response to a motion of the shift actuator in a direction away from the corresponding maximum reduction ratio position. A control unit stores a predetermined shift pattern which provides a target value in the turbine revolution speed versus one of various combinations of throttle opening degree and vehicle speed values and governs which position the shift actuator is to take in accordance with this predetermined shift pattern.
According to this known ratio control, the limit is imposed on suppressing overshoot in turbine revolution speed at rapid acceleration of the vehicle from a standstill after the throttle opening degree has been increased rapidly. This is derived from the fact that the maximum reduction ratio is kept until the vehicle speed reaches an upshift vehicle speed predetermined by the shift pattern and thus the turbine revolution speed is subject to a rapid increase in the vicinity of this upshift vehicle speed.
An object of the present invention is to improve a ratio control such that the overshoot mentioned above is suppressed or reduced satisfactorily.